When Kenneth Boxer called, you could hear the sense of betrayal in his voice.

Boxer is the owner of the Italian restaurant Palazzio in Santa Barbara, Calif., a restaurant known for its generous plates of pasta and servers who might spontaneously sing along to Dean Martin’s “That’s Amore” on a Saturday night. He he was calling to share his story of a scam he fears might be happening in restaurants across the country.

Recently, Boxer said, he discovered that a server he had employed for about 18 years was double charging customers for tips.